Force limited coupling

ABSTRACT

Disclosed herein is a hydrostatic drive unit controlled by a spring-loaded device which serves, in effect, as a mechanical safety valve preventing or limiting the buildup of undesirable or excessive pressure in the hydrostatic unit. Also disclosed herein is such a control device comprising a force-limiting coupling which connects the ends of a pair of parallel links or rods. When an axial force exerted in either direction on one of the links attains a predetermined force value, a spring yieldably affords overtravel or relative movement of one of the control links with respect to the other to prevent transmission of excessive forces.

United States Patent Inventors 9 f 2,625,838 1/1953 Dillard 74/582 KirkRelmers, both of Llnwln,Nebr- 2,896,411 7 1959 Bowers et al. 60/52 USP[21] App]. No. 859,254 3,198,301 8/1965 Randall 74/582 [22] Filed d33312931997619 3,323,607 6/1967 Futamata 74/471 X [451 Palm FOREIGNPATENTS [73] Assignee Outboard Marine Corporation Waukegan, 111.,322,845 2/1963 France 180/648 Continuation-impart of application Ser.No. Primary Examiner-William F ODea May 2, 126 9, I l 9 hglElg I 1Assistant ExaminerF. D. Shoemaker Attorneys-Robert E. Clemency, John W.Michael, Gerrit D.

Foster, Bayard H. Michael, Robert K. Gerling, Paul R. Puerner, Joseph A.Gemignani, Andrew 0. Riteris and S encer B. M'chael [S4] FORCE LIMITEDCOUPLING p I m 4 Claims, 4 Drawing Figs. 3

[52] US. Cl 74/471, ABSTRACT; Disclosed herein is a hydrostatic driveunit con- 60/53 74/47l 9 180/6- 8 i trolled by a spring-loaded devicewhich serves, in effect, as a [51] lnt.C1 605g 9/00 i h nical safetyvalve preventing or limiting the buildup of [50] Field of $8811! 74/582,4 7 l 1 desirable o excessive pressure in the hydrostatic unit, Also 9-3 0 B disclosed herein is such a control device comprising a force-91/413 1 limiting coupling which connects the ends of a pair of parallel56 R d 1 links or rods. When an axial force exerted in either directionI l e H 1 on one of the links attains a predetermined force value, aUNITED STATES PATENTS 1 spring yieldably affords overtravel or relativemovement of 1,304,955 5/1919 Fowler 74/582 X one of the control linkswith respect to the other to prevent 2 081407 4/1936 Cremer 74/582 X 1transmission of excessivejorces.

if 2 l 1 W1 /8 48 24 \j FORCE LIMITED COUPLING This application is acontinuation-in-part of our earlier application Ser. No. 821,214 filedMay 2, I969 now abandoned.

BACKGROUND OF THE INVENTION The invention relates to controls forhydraulic or hydrostatic drive units which develop internal pressures inaccordance with the load experienced by the output shaft. In operationand in response to the encountering of a greater load, the pressurebuilds up within the hydrostatic unit and can tend to return the swashplate toward neutral. Thus, as the load builds up, the operator mustapply a proportional counterforce to meet the increased load in anattempt to retain the output speed setting of the hydrostatic unit or atleast to retain sufficient output from the hydrostatic unit to maintainsome output speed. Under such circumstances, if the operator or userapplies increasing force to the control to meet an increasing loadexperienced by the hydrostatic unit, the result can be a buildup ofhydraulic pressure within the hydrostatic unit to excessive levels whichcan cause damage or excessive wear to the hydrostatic unit.

In order to alleviate this situation, various hydrostatic transmissionshave, in the past, included pressure relief valves which are expensiveand have operating deficiencies, such as seal problems. In addition,when such safety valves operate, the oil is heated providing an energyloss and a temperature problem.

In addition, the invention also relates to couplings for connecting twoparallel links or push rods which transmit linear forces.

SUMMARY OF THE INVENTION It is an object of the invention to provide aforce-limiting mechanical coupling or connection which is providedbetween a hydrostatic transmission and the transmission control memberand which protects the transmission from overload and eliminates theneed for a pressure relief valve in the transmission.

The invention provides a control for a hydrostatic transmission or driveunit, which control affords limitation of the operating or controllingforce applied by the operator to the transmission unit, therebypreventing pressure overloading of the transmission unit. Variousmechanical arrangements for controlling the hydrostatic unit can beprovided which will yield, either instantaneously or gradually, so at toprevent excessive loading of the hydrostatic drive unit.

It is a further object of the invention to provide a coupling forconnecting parallel shafts or links, which coupling limits thetransmission of forces.

The invention also provides a coupling for the previously mentionedhydrostatic unit control, or for other uses, which coupling limits thetransmission of forces from one link to another to a predetermined, safevalue to minimize damage to the controlled unit. When the loading forceson one coupling member exceed the predetermined force level, a springyieldably affords overtravel or relative movement of one of the couplingmembers with respect to the other.

More specifically in one disclosed construction, the coupling connectstwo parallel links or rods and includes a compression spring locatedbetween two washers carried by one of the control rods. The washers arelocated interiorly of fixed guides or abutments carried by the othercontrol rod. The first mentioned control rod extends through the washersand spring and is movable in coaxial apertures in the two guides. Whenforces are exerted on the first-mentioned control rod, one of thewashers bears against the spring to transmit force to the opposite guideand thus the other control rod. When the predetermined force level isattained, the spring compresses and permits overtravel of thefirst-mentioned control rod through the apertures in the guides.

Further objects and advantages of the invention will become apparentfrom the following description and accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary sectional view of acoupling in accordance with the invention.

FIG. 2 is a sectional view taken along the line 22 of FIG. 1.

FIG. 3 is a fragmentary perspective view of the two control rodassemblies of the invention in use in a speed and steering control forthe vehicle.

FIG. 4 is an elevational view of a hydrostatic transmission unitconnected to a control in accordance with the invention.

DETAILED DESCRIPTION Shown in FIG. 3 are a pair of hydrostatictransmission units 54 and 56 which are arranged to drive a vehiclethrough output shafts 60 adapted to be connected to the wheels or thetracks of a vehicle. Each of the transmissions 54 and 56 includes anactuating member which can be displaced in either direction from aneutral operating position to respectively provide forward and rearwardoperation at speeds which increase with increasing displacement from theneutral position. One form of such hydrostatic unit, shown in thedisclosed constructions, includes an actuating member in the form of aninterior swash or wobble plate (not shown) connected to a swash plate ortransmission lever or member 58 operable to vary the location of theswash plate. Each of the swash plate or transmission levers 58 isconnected to a control member 42 by means affording coordinated speedand direction control of the output shafts 60. Various arrangements canbe employed to obtain coordinated speed and direction control. When thehydrostatic units experience excessive loading, said means alsofunctions to limit the forces applied to the transmission levers 58 andthereby to the swash plates by affording lost motion in the controllinkage, thereby acting in the nature of a safety valve to prevent thebuildup of excessive hydraulic pres sures within the hydrostatic unit.Various arrangements can be utilized to provide lost motion in thecontrol incident to development of predetermined pressure in thehydrostatic unit.

In the arrangement shown in FIGS. 1 through 3, the control member 42comprises a handle or short cross-shaft at the top, a vertical post orcontrol stick 44 which is rotatably supported for movement about avertical axis in a sleeve 46. The sleeve 46 and control stick 44 arerotatably supported for tilting movement about a horizontal axis byopposed trunnions 47 which are joumaled in pillow blocks 48 carried by aframe 50. At its bottom, the control stick 44 is connected to a bracket52.

As already indicated, the control member 42 can be connected to thehydrostatic unit to prevent excessive pressure buildup in thehydrostatic unit by various arrangements affording lost motion inresponse to the input of force, either from the operator or from thecontrolled hydrostatic unit, above a predetermined level. In theconstruction disclosed in FIGS. 1 through 3, such means is in the formof a pair of control rod or link assemblies 62 and 64 which arerespectively connected to the swash plate levers 58 by L-shapedcouplings 72 and to the bracket 52 by T shaped couplings 66 havingthreaded portions 68 which extends through apertures 70 in the bracket52.

Each of the control rod assemblies 62 and 64 includes a coupling 10which connects first and second control rod portions or links 12 and 14.Each coupling 10 includes a pair of guides or abutments l6 and I8including apertures 19 and 21 receiving the control rod portion I2. Theguides 16 and I8 are also each provided with an aperture 20 and 22 andare secured in spaced relationship to the control rod portion 12 bywelds 23 such that the apertures 20 and 22 are aligned in coaxialrelation to receive the second control rod portion 14.

In accordance with the invention, means are provided which cooperatewith the guides for affording relative movement or overtravel of one ofthe control rod portions with respect to the other of the control rodportions when loading forces exerted on either of the rod portions 12 or14 exceed a predetermined force magnitude. In the disclosed constructionthe means includes a preloaded compression spring 24 which is telescopedover or arranged around the rod portion 14 and located between theabutments 16 and 18. The means also includes means on the second rodportion 14 for engaging the spring 24 to transmit loading forces fromthe second rod to the spring. As disclosed, the means comprises abushing 26 which extends through the aperture and can be welded at 28 orotherwise secured to rod portion 14. The means also includes two washers29 and 30 which are carried by the second control rod portion 14 and arelocated between the ends of the spring 24 and the guides 16, 18.

The invention also includes means for limiting travel in one directionof the rod portion 14. As disclosed, the means includes a bushing 32which extends through aperture 22 and engages the washer 30. The meansalso includes a threaded portion 36 on the end of the second rod portion14 and a nut 38 which bears against the end 40 of bushing 32. The washer40 and nut 38 prevent the rod portion 14 from being pulled completelythrough the aperture 22 and also facilitate assembly of the spring 24and washers 29, 30. Alternatively, the means for limiting travel of therod portion 14 can be a fixed abutment on the rod portion 14.

In operation of the control apparatus shown in FIG. 3, forward orrearward control member movement about the axis of the trunnions 47 orsteering movement of the control member about the axis of the controlstick 44 will cause an axial force to be exerted on the control rodassemblies 62 and 64. When the forces on the control rod assembliesexceed a predetermined safe force limit, as for instance when thevehicle is in rough terrain, climbing a hill, or carrying a heavy load,etc., the springs 58 will compress and provide overtravel or relativemovement of the first rod portions 12 with respect to the second rodportions 14, as well as movement of the swash plate levers 58 while thecontrol member remains stationary, thus preventing increasing forcesapplied by the operator from reaching the levers 58 and therebyminimizing the possibility of damage to the transmissions.

More specifically, a pulling force exerted on the coupling 10, as forinstance, by clockwise movement of the control member 42 about thetrunnions 47, will cause the springs 24 to be urged against guides 16 bythe washers 30. When the predetermined force level is exceeded, thesprings 24 will yieldably afford overtravel of rods 14 to the leftrelative to the rods 12 with the bushings 28 sliding through theapertures 20 and the bushings 32 sliding through the apertures 22. Apushing force on control rod portions 14 caused by counterclockwisemovement of the control member 42 about the trunnions 47 will cause thesprings 24 to be urged against the guides 18 by the bushings 28 andwashers 29. When the predetermined force level is exceeded, the rodportions 14 will move to the right relative to the rods 12 and theguides 16 and 18.

While the above arrangement provides a particularly satisfactory controlarrangement, various other arrangements can be employed to preventexcessive buildup of pressures in a hydrostatic unit consequent to theapplication of increasing load on the output of the hydrostatic unit andattempted operator action to meet the load. Such means could employ ayieldable elastomeric or rubber connection or spring, or a pneumatic orhydraulic spring with a compressible fluid and in the form of a cylinderaffording lost motion above a predetermined force value.

It should also be noted that the lost motion feature can be providedanywhere in the linkage between the actuating member of the hydrostaticunit and the control member which is grasped by the operator.

It should be further noted that the lost motion action afforded by thespring means is applicable to prevent excessive pressure buildup in asingle hydraulic transmission unit independently of an integrated systemincluding more than one such unit.

Thus, there is shown in FIG. 4 a hydrostatic unit 75 having an actuatingmember with a lever or element 77 which is fixed thereto and moves withthe actuating member to either side of a neutral position. The lever 77has pivotally fixed thereto a control member 79 which has, at the outerend thereof, a control handle 81. Alternatively, the control member 79could be connected to a linkage having a remote actuator.

Means are provided for obtaining lost motion between the lever 77 andthe control member 79 or handle 81 when the hydraulic unit 75experiences an excessive load so as to prevent the operator fromapplying sufficient force to meet the lead and thereby cause excessivebuildup of pressure within the hydrostatic unit. In the constructiondisclosed in FIG. 4, such means includes a connection 83 which joins thecontrol member 79 and the transmission member lever 77 and which affordspivotal movement which can be lost" between the lever 77 and the controlmember 79 or handle 81. In addition, such means also includes springmeans operating between the handle 81 or control member 79 and the lever77, which spring means accommodates lost angular movement or motion whenthe force applied by the operator through the control member 79 to rockthe lever 77 exceeds a predetermined level or magnitude, therebyavoiding excessive pressure buildup in the hydrostatic unit.

While various spring means can be employed, in the construction shown inFIG. 4, each of the control member 79 and transmission lever 77 includerespective oppositely extending wings or ears 85 and 86 with the wings85 of the control member 79 facing the wings 86 of the transmissionlever 77. Each wing 85 is suitably recessed as at 87 to respectivelyreceive the ends of a pair of preloaded helical compression springs 89and to thereby retain the springs in proper operating position. Inaddition, the recesses 87 in the wings 86 communicate with bores 88, forpurposes still to be described.

More particularly, means are provided for preloading each of the spring89. Various arrangements can be employed. In the disclosed construction,such means is in the form of T- shaped members 82 each having a head 84and a stem 90. The heads 84 can be received in the recesses 87 of thewings 85 for guidance purposes and are engaged with both the top of thesprings 89 and, when the control member and lever are in neutralposition, with the base of the recesses 87 in the wings 85. The stems 90extend through the springs 89 and through the bores 88 to below thewings 86. The lower ends of the stems 90 are threaded and locknuts areemployed on the threaded stems below the wings 86, thereby to bothpreload the springs and to locate the heads 84 in proper positionrelative to the wings 85 so that when the applied forces are below thepreload of the springs 89, the control member 77 and the lever 79 willact in unison. However, when the forces applied between the member 79and lever 77 exceed the preload on the springs 89, relative movementwill occur between the lever 77 and the member 79 so as to avoidexcessive buildup of pressure in the connected associated hydrostaticunit.

In operation, movement of the handle 81 or control member 79 to the leftor right will cause corresponding movement of the transmission lever 77.However, when the force applied to the handle 81 or control member 79 isincreased above a predetermined value in order to meet an increasingload, lost angular movement will occur to prevent further increasedapplication of force to the transmission lever 77 from the controlmember 79 and thereby limit the pressure level in the hydrostatic unit75. Thus, there is provided an effective mechanical safety valve toprevent excessive pressure in the hydrostatic unit 75.

While both specifically disclosed embodiments include compressionsprings, the invention extends to various kinds of preloaded springdevices including tension and leaf springs and, as before mentioned, toelastomeric springs and hydraulic and pneumatic springs provided bycompressible fluid, In addition, the invention extends to variouslinkages including rectilinear and angular lost motion connections andlinkages whereby to avoid the application of excessive force to ahydrostatic transmission actuating lever or member.

ininns no 1 Various of the features of the following claims.

lclaim:

l. A control system comprising a control member, means for supportingsaid control member for movement about horizontal and vertical axes, ahydrostatic transmission, said transmission having an operating lever, afirst rod operably connected to said operating lever and a second rodoperably connected to said control member, and a linkage connecting saidfirst and second rods and including mechanical means interposed betweensaid first and second rods for limiting force transmission from one ofsaid rods to the other of said rods to a predetermined force level.

2. A control system comprising a control member, means for supportingsaid control member for movement about horizontal and vertical axes, ahydrostatic transmission having an operating lever, a first rod operablyconnected to said operating lever, a second rod operably connected tosaid control member, first and second abutments carried by and securedto said first rod, said abutments being spaced longitudinally of saidfirst rod, coaxial apertures in each of said first invention are setforth in the and second abutments, said apertures receiving said secondrod, a spring arranged around said second rod and located between saidabutments, and means on said second rod engageable with said spring tocompress said spring and thereby to limit force transmission from one ofsaid rods to the other of said rods to a predetermined force level.

3. A drive comprising a hydrostatic transmission including a membermovable in opposite directions from a neutral position, a controlmember, and means connecting said control member and said transmissionmember and including spring means for afiording lost motion between saidmembers upon the attempted transmission of force between said membersabove a predetermined force magnitude.

4. A drive comprising a hydrostatic transmission including a membermovable in opposite directions from a neutral position, a controlmember, and a mechanical linkage connecting said control member and saidtransmission member including means for preventing transmission of forcetherebetween above a predetermined force magnitude.

1. A control system comprising a control member, means for supportingsaid control member for movement about horizontal and vertical axes, ahydrostatic transmission, said transmission having an operating lever, afirst rod operably connected to said operating lever and a second rodoperably connected to said control member, and a linkage connecting saidfirst and second rods and including mechanical means interposed betweensaid first and second rods for limiting force transmission from one ofsaid rods to the other of said rods to a predetermined force level.
 2. Acontrol system comprising a control member, means for supporting saidcontrol member for movement about horizontal and vertical axes, ahydrostatic transmission having an operating lever, a first rod operablyconnected to said operating lever, a second rod operably connected tosaid control member, first and second abutments carried by and securedto said first rod, said abutments being spaced longitudinally of saidfirst rod, coaxial apertures in each of said first and second abutments,said apertures receiving said second rod, a spring arranged around saidsecond rod and located between said abutments, and means on said secondrod engageable with said spring to compress said spring and thereby tolimit force transmission from one of said rods to the other of said rodsto a predetermined force level.
 3. A drive comprising a hydrostatictransmission including a member movable in opposite directions from aneutral position, a control member, and means connecting said controlmember and said transmission member and including spring means foraffording lost motion between said members upon the attemptedtransmission of force between said members above a predetermined forcemagnitude.
 4. A drive comprising a hydrostatic transmission including amember movable in opposite directions from a neutral position, a controlmember, and a mechanical linkage connecting said control membEr and saidtransmission member including means for preventing transmission of forcetherebetween above a predetermined force magnitude.